Drilling machines are used in a number of surgical procedures, for example, in making holes in bones for bone screws and in drilling out the medulla or marrow areas of bones. In the latter procedure, in particular, it is normally necessary to use an angle frame, i.e., a device which will translate the rotation of the drilling machine to turn a drill having an axis at an angle to the axis of rotation of the drilling machine. Such devices are known and are commercially available.
To improve the precision of surgical drilling, a technique has been developed in recent years in which the bone is positioned in the path of radiation from an X-ray machine with video amplifier control. Various types of aiming devices can be used to verify and monitor the position and direction of the drill bit. See, for example, Frigg et al., U.S. Pat. No. 4,803,976.
Such aiming devices have suffered from the disadvantage that during the actual drilling procedure the position of the drill bit cannot be observed directly because the drilling machine covers the visual field of the video amplifier. A further disadvantage of covering the field of vision is that the automatic control of radiation by the amplifier raises the radiation intensity to penetrate the metal of the drilling machine. This increased radiation naturally also affects the hand of the surgeon guiding the drilling machine. Secondary radiation occurring through reflection from the metal is of particular danger.